1. Field of the Invention
The present invention relates to an improved process for manufacturing 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb), or more particularly to an improved process for the production of HCFC-244bb by reacting 2-chloro-3,3,3,-trifluoropropene (HCFO-1233xf) with hydrogen fluoride, in a liquid phase reaction vessel in the presence of hydrogen chloride and a liquid phase fluorination catalyst. The HCFC-244bb is an intermediate in the production of 2,3,3,3-tetrafluoropropene (HFO-1234yf) which is a refrigerant with low global warming potential.
2. Description of the Related Art
Fluorocarbon based fluids have found widespread use in industry in a number of applications, including as refrigerants, aerosol propellants, blowing agents, heat transfer media, and gaseous dielectrics. Because of the suspected environmental problems associated with the use of some of these fluids, including the relatively high global warming potentials associated therewith, it is desirable to use fluids having the lowest possible greenhouse warming potential in addition to zero ozone depletion potential. Thus there is considerable interest in developing environmentally friendlier materials for the applications mentioned above. Tetrafluoropropenes, having zero ozone depletion and low global warming potential, have been identified as potentially filling this need. However, the toxicity, boiling point, and other physical properties in this class of chemicals vary greatly from isomer to isomer. One tetrafluoropropene having valuable properties is 2,3,3,3-tetrafluoropropene (HFO-1234yf). HFO-1234yf has been found to be an effective refrigerant, heat transfer medium, propellant, foaming agent, blowing agent, gaseous dielectric, sterilant carrier, polymerization medium, particulate removal fluid, carrier fluid, buffing abrasive agent, displacement drying agent and power cycle working fluid. Thus, there is a need for new manufacturing processes for the production of tetrafluoropropenes and in particular 2,3,3,3-tetrafluoropropene.
In U.S. Pat. No. 2,931,840, methyl chloride has been pyrolyzed along with CF2HCl at 800° C. to give a product stream that contains about 15% of CF3CF═CH2. HFO-1234yf has also been made by the dehydrofluorination of CF3CHFCH2F with KOH in butyl ether (Chem. Abstr. 1961: 3490, and by the reaction of CF3CF2CH2OH with hydrogen in U.S. Pat. No. 4,900,874.
It would be advantageous to have a process for the manufacture of HFO-1234yf that is continuous, and which uses readily available raw materials. As the prior art processes fail in one or more of these desirable features, more advantageous routes are desired, especially those amenable to large-scale manufacture. One of the steps in recent manufacturing processes for HFO-1234yf requires the fluorination HCFO-1233xf with hydrogen fluoride to form 2-chloro-1,1,1,2-tetrafluoropropane (HCFC-244bb). In the liquid phase fluorination of HCFO-1233xf to produce HCFC-244bb, no HCl is produced because the reaction is strictly a hydrofluorination reaction where HF adds across the double bond. This lack of HCl by-product formation is unique when compared to other well-known liquid phase fluorination reactions that produce CFCs (e.g. CFC-12), HCFCs (e.g. HCFC-22, HCFC-142b), and HFCs (e.g. HFC-143a, HFC-245fa). This is because these reactions involve a halogen exchange, in whole or in part. That is, F− replaces a Cl− on the molecule. It is advantages to run liquid phase fluorination reactions at relatively elevated pressures which are easily achieved by the formation of HCl. Because it is non-condensable at the desired reaction conditions, HCl formation also increases mixing in the reactor and it readily comes out in the overhead of the catalyst stripper and helps by carrying out the fluorinated product. Because no HCl is produced in the reaction of HCFO-1233xf to HCFC-244bb there is less mixing in the reactor which may decrease conversion and promote by-product formation. In addition, the reactor is more difficult to control because there is no HCl to create high pressure nor to help carry out the HCFC-244bb that is formed.
In the present invention HCl is co-fed to the reactor along with the HF and HCFO-1233xf. The reactor and catalyst stripper runs like a typical liquid phase fluorination reaction that produce CFCs, HCFC's, and HFCs as described above. This has a number of benefits. It enables the reaction to achieve and run at relatively elevated pressures, it increases mixing in the reactor, and it readily leaves the reactor in the overhead of the catalyst stripper carrying with it product HCFC-244bb. The HCl co-feed is essentially inert, does not participate in the fluorination reaction, and produces little or no unwanted by-products. Any source of HCl can be used in the reaction. Preferably HCl produced in-situ from a prior step in a multi-step process to produce HFO-1234yf is used as the source. An example of such a step involves the fluorination of 1, 1,2,3-tetrachloropropene or 1,1,1,2,3-pentachloropropane with HF, optionally but preferably in the presence of a fluorination catalyst to form HCFO-1233xf intermediate and HCl. Then, all or only a portion of the HCl produced in this step is co-fed into the liquid phase fluorination reactor that produces HCFC-244bb.